Stents having radiopaque mesh

ABSTRACT

A stent including a mesh made of strands. The mesh has at least one radiopaque strand and at least one non-radiopaque strand, and the at least one radiopaque strand and the at least one non-radiopaque strand each have different diameters. Each strand has an index of wire stiffness EI, where EI is the mathematical product of the Young&#39;s modulus (E) and the second moment of area (I). The EI of all strands in the mesh is no more than five times the EI of the strand having the smallest EI of any of the strands.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.15/478,161, filed Apr. 3, 2017, which is a continuation of U.S.application Ser. No. 15/137,364, filed Apr. 25, 2016, now U.S. Pat. No.9,610,181, which is a continuation of U.S. application Ser. No.13/792,344, filed Mar. 11, 2013, now U.S. Pat. No. 9,320,590, which is acontinuation of U.S. application Ser. No. 13/407,044, filed Feb. 28,2012, now U.S. Pat. No. 8,394,119, which is a continuation of U.S.application Ser. No. 11/708,651, filed Feb. 20, 2007, now U.S. Pat. No.8,152,833, which claims the benefit of U.S. Provisional Application No.60/775,818, filed Feb. 22, 2006, the contents of each of which arehereby incorporated by reference herein.

TECHNICAL FIELD

The present technology relates to embolic protection systems, and, moreparticularly, to embolic protection systems for use in blood vessels.

BACKGROUND

Vessels are commonly treated to reduce or eliminate narrowings caused byarteriosclerotic disease. Interventional treatments can include use ofballoon angioplasty, stenting, thrombectomy, atherectomy, and otherprocedures. During treatment particulate debris can be generated at thetreatment site. Infarcts, strokes, and other major or minor adverseevents are caused when debris embolizes into vasculature distal to thetreatment site.

To prevent embolization of debris, embolic protection devices have beendeveloped. During a procedure such devices can be placed distal orproximal to the treatment site. Embolic protection devices can removeemboli from the bloodstream by filtering debris from blood, by occludingblood flow followed by aspiration of debris, or can cause blood flowreversal to effect removal of debris. The shape, length and othercharacteristics of an embolic protection device are typically chosenbased on the anatomical characteristics in the vicinity of the treatmentsite. However, some anatomies present specific challenges due to theanatomical shape or configuration.

Difficulties can arise where embolic protection devices are not properlydeployed within the anatomy. For example, if a device does not properlyengage a lumenal wall, leaving a gap, then particulate matter entrainedin a fluid in the lumen can bypass the protection device. It would be anadvantage to be able to visualize whether or not there are gaps betweenthe embolic protection device and the lumenal wall. Also, when aprotection device is being advanced or withdrawn from a lumen it mayengage with an obstruction. The obstruction may be a stent that has beenplaced in a blood vessel, an area of plaque build-up, lumen tortuosity,or other structure. The operator of the embolic protection device mayneed to employ different techniques to advance or withdraw the devicedepending on the cause of engagement. Thus, it would be advantageous forthe operator to be able to visualize the exact location of the device inthe lumen.

Difficulties can also arise when recovering an embolic protectiondevice. One problem that can occur is that the embolic protection devicemay require excessive force during recovery, for example when drawingthe device into a recovery catheter. The causes of such excessive forcecan vary. For example the device could be filled with embolic debris andthereby not fit into the lumen of a recovery catheter, the device may becaught on a structure such as a stent or a catheter tip, or othercauses. It would be advantageous to the operator to visualize theembolic protection device so that appropriate actions can be taken so asto successfully recover the device. Further discussion of these issuesis provided in U.S. Patent Publication No. 2002/0188314 A1, by Andersonet. al., entitled “Radiopaque Distal Embolic Protection Device”, thecontents of which are incorporated herein by reference.

The current art employs a variety of approaches to solve the problem ofvisualizing an embolic protection device in a patient. All of thecurrent approaches have limitations. For example, some devices haveradiopaque coatings; however coatings may become separated from theunderlying substrate. Radiopaque filler materials have been employed inpolymer film devices; however the fillers detract from the mechanicalproperties of the films and the filler/film composites, being thin, arenot very visible. Strands of drawn filled tubing (DFT) have been usedand have good mechanical and radiopacity characteristics; however DFT isexpensive. Individual strands of radiopaque wire, such as platinum,gold, tungsten, and their alloys have good radiopacity but can haveunsuitable strength or elastic yield limits, and when comprising aportion of the wires in a woven structure such as a braid, can alter thebraid wire spacing in the vicinity of the strand of radiopaque wire dueto differing mechanical properties compared to neighboringnon-radiopaque wires. For some filter devices, uniform wire spacing isdesired and altered braid wire spacing can cause unacceptably largepores in the braid.

Accordingly, a need exists for an embolic protection device havingimproved radiopacity that is inexpensive, durable, provides visibilityto the appropriate regions of the device, and which uses technology thatdoes not compromise the performance of the device.

SUMMARY

According to one aspect of the present invention, an embolic protectiondevice comprises a woven mesh comprising radiopaque and non-radiopaquewires. The mechanical properties of the radiopaque wires are selected tomatch the mechanical properties of the non-radiopaque wires. Thenon-radiopaque wires can be superelastic. The radiopaque wires are woveninto pre-programmed locations so that after processing the woven meshinto a device the radiopaque wires will concentrate at a preferredlocation within the device. A method is provided in which the deviceoperator visualizes the radiopaque wires so as to guide how the deviceis utilized in a patient.

The invention provides a device for filtering emboli from blood flowingthrough a lumen defined by the walls of a vessel in a patient's body,comprising: a filter element being expandable from a collapsedconfiguration when the filter element is restrained to an expandedconfiguration when the filter element is unrestrained, wherein thefilter element comprises a mesh comprising strands, each strand having adiameter, the mesh comprising at least one radiopaque strand and atleast one non-radiopaque strand, and wherein each strand has an index ofwire stiffness EI, where EI is the mathematical product of the Young'smodulus (E) and the second moment of area (I), and wherein the largestEI of a strand is no more than five times the smallest EI of a strand.

The invention provides a method of deploying a device for filteringemboli from blood flowing through a lumen defined by the walls of avessel in a patient's body comprising: providing the device forfiltering emboli, the device comprising a filter element beingexpandable from a collapsed configuration when the filter element isrestrained to an expanded configuration when the filter element isunrestrained, wherein the filter element comprises a mesh comprisingstrands, each strand having a diameter, the mesh comprising at least oneradiopaque strand and at least one non-radiopaque strand, and whereineach strand has an index of wire stiffness EI, where EI is themathematical product of the Young's modulus (E) and the second moment ofarea (I), and wherein the largest EI of a strand is no more than fivetimes the smallest EI of a strand; delivering the device percutaneouslyto a region of interest in the lumen of the patient's body; and usingfluoroscopy to visualize the filter element in the lumen of thepatient's body.

The invention provides a mesh comprising strands, each strand having adiameter, the mesh comprising at least one radiopaque strand and atleast one non-radiopaque strand, and wherein each strand has an index ofwire stiffness EI, where EI is the mathematical product of the Young'smodulus (E) and the second moment of area (I), and wherein the largestEI of a strand is no more than five times the smallest EI of a strand.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of the invention may be betterunderstood by referring to the following description in conjunction withthe accompanying drawings.

FIGS. 1A to 1C illustrate conceptually a partial plan view of braidedtubular mesh having radiopaque and non-radiopaque wires in accordancewith the present invention.

FIG. 2 illustrates conceptually a side view of a filter formed frombraided tubular mesh in accordance with the present invention.

FIG. 3 illustrates conceptually a method for forming a filter frombraided tubular mesh in accordance with the present invention.

FIGS. 4A and 4B illustrate conceptually plan views of braided mesh inaccordance with the present invention.

FIGS. 5A to 5E illustrate cross sectional or side views of wires inaccordance with the present invention.

DETAILED DESCRIPTION

The invention provides a device for filtering emboli from blood flowingthrough a lumen defined by the walls of a vessel in a patient's body,comprising: a filter element being expandable from a collapsedconfiguration when the filter element is restrained to an expandedconfiguration when the filter element is unrestrained, wherein thefilter element comprises a mesh comprising strands, each strand having adiameter, the mesh comprising at least one radiopaque strand and atleast one non-radiopaque strand, and wherein each strand has an index ofwire stiffness EI, where EI is the mathematical product of the Young'smodulus (E) and the second moment of area (I), and wherein the largestEI of a strand is no more than five times the smallest EI of a strand.

In one embodiment, the device further comprises an elongate supportmember and the filter element is carried on a portion of the elongatesupport member. In another embodiment, the filter element has proximaland distal portions and a central portion, the filter element having ashape in the expanded configuration which defines a cavity having aproximal facing opening. In one embodiment, the filter element has aproximal facing opening portion and this portion is radiopaque.

The filter element may be self-expanding or self-contracting. The meshmay be tubular and/or braided. In one embodiment, each strand has around cross-section. In another embodiment, the mesh comprises only twotypes of strands, a first type being a radiopaque strand and having adiameter D1 and a second type being a non-radiopaque strand and having adiameter D2. In one embodiment, the Young's modulus of the radiopaquestrand and the Young's modulus of the non-radiopaque strand differ by 10percent or more. In another embodiment, the Young's modulus of theradiopaque strand and the Young's modulus of the non-radiopaque stranddiffer by 20 percent or more.

In one embodiment, the mesh comprises more radiopaque strands thannon-radiopaque strands. In another embodiment, the mesh comprises morenon-radiopaque strands than radiopaque strands. In embodiments of theinvention, the largest EI of a strand is no more than four times thesmallest EI of a strand, the largest EI of a strand is no more than twotimes the smallest EI of a strand, the largest EI of a strand is no morethan 1.5 times the smallest EI of a strand, or the largest EI of astrand is no more than 1.3 times the smallest EI of a strand.

In embodiments of the invention, the mesh comprises pores and when themesh is at rest in free space no pore has an area more than five timesthe mesh pore size, when the mesh is at rest in free space no pore hasan area more than four times the mesh pore size, when the mesh is atrest in free space no pore has an area more than three times the meshpore size, when the mesh is at rest in free space no pore has an areamore than two times the mesh pore size, when the mesh is at rest in freespace no pore has an area more than 1.5 times the mesh pore size, orwhen the mesh is at rest in free space no pore has an area more than 1.2times the mesh pore size. The mesh pore size is the average area of fivepores serially adjacent to the pore.

In embodiments of the invention, the mesh comprises at least two typesof strands, each strand having a round cross-section, a first type ofstrand being a radiopaque strand and having a diameter D1 and a secondtype of strand being a non-radiopaque strand and having a diameter D2,diameter D1 being larger than diameter D2, wherein the mesh comprisespores and when the mesh is at rest in free space no pore adjacent to astrand having a diameter D1 has an area more than five times the meshpore size, the mesh pore size being the average area of five poresserially adjacent to the pore. In other related embodiments, when themesh is at rest in free space no pore adjacent to a strand having adiameter D1 has an area more than four times the mesh pore size, morethan three times the mesh pore size, more than two times the mesh poresize, more than 1.5 times the mesh pore size, or more than 1.2 times themesh pore size.

In one embodiment, the at least one radiopaque strand is made ofhomogeneous metal or metal alloy. In another embodiment, the at leastone radiopaque strand is selected from the group consisting of strandsmade of gold, platinum, tungsten, tantalum, and alloys thereof. Otherradiopaque substances may be used. In an embodiment, the at least onenon-radiopaque strand is made of metal. In one embodiment, the at leastone non-radiopaque strand is selected from the group consisting ofstrands made of stainless steel and nitinol. Other non-radiopaquesubstances may be used. In one embodiment, the at least onenon-radiopaque strand is superelastic.

In embodiments of the invention, the largest diameter of a strand is nomore than five times the smallest diameter of a strand, the largestdiameter of a strand is no more than four times the smallest diameter ofa strand, the largest diameter of a strand is no more than two times thesmallest diameter of a strand, or the largest diameter of a strand is nomore than 1.5 times the smallest diameter of a strand. In oneembodiment, the largest diameter of a strand is no more than two timesthe smallest diameter of a strand, and the largest EI of a strand is nomore than two times the smallest EI of a strand.

In one embodiment, the at least one radiopaque strand is a monofilament.In one embodiment, the at least one non-radiopaque strand is amonofilament. In another embodiment, the mesh comprises only two typesof strands, a first type being a radiopaque strand and having a diameterD1 and a second type being a non-radiopaque strand and having a diameterD2, and both the first and second types of strands are monofilaments. Inone embodiment, the at least one radiopaque strand is a multifilamentwire. In another embodiment, at least one strand is a monofilament wirefrom which some material has been removed in the form of slots. In oneembodiment, the at least one non-radiopaque strand is made of nitinol.

The invention provides a method of deploying a device for filteringemboli from blood flowing through a lumen defined by the walls of avessel in a patient's body comprising: providing the device forfiltering emboli, the device comprising a filter element beingexpandable from a collapsed configuration when the filter element isrestrained to an expanded configuration when the filter element isunrestrained, wherein the filter element comprises a mesh comprisingstrands, each strand having a diameter, the mesh comprising at least oneradiopaque strand and at least one non-radiopaque strand, and whereineach strand has an index of wire stiffness EI, where EI is themathematical product of the Young's modulus (E) and the second moment ofarea (I), and wherein the largest EI of a strand is no more than fivetimes the smallest EI of a strand; delivering the device percutaneouslyto a region of interest in the lumen of the patient's body; and usingfluoroscopy to visualize the filter element in the lumen of thepatient's body. The device used in this method can be any of theembodiments described herein. In one embodiment, the filter element hasproximal and distal portions and a central portion, the filter elementhaving a shape in the expanded configuration which defines a cavityhaving a proximal facing opening, the filter element has a proximalfacing opening portion and this portion is radiopaque, and the proximalfacing opening portion of the filter element is visualized to confirmthat this portion is adequately deployed against the walls of thevessel.

The invention provides a mesh comprising strands, each strand having adiameter, the mesh comprising at least one radiopaque strand and atleast one non-radiopaque strand, and wherein each strand has an index ofwire stiffness EI, where EI is the mathematical product of the Young'smodulus (E) and the second moment of area (I), and wherein the largestEI of a strand is no more than five times the smallest EI of a strand.The mesh can be any of the embodiments described herein in connectionwith the mesh that is part of the device for filtering emboli.

In the discussion below the invention is described using as examplesfilters comprised of braided metal strands. It is to be understood thatthe invention is not limited to the examples below. For example, themesh of the invention can be comprised of strands that are woven,non-woven, or knitted to form the mesh. The mesh can have uniform strandspacing so as to define a structure with relatively uniformly sizedopenings between strands or can have variable strand spacing so as todefine a structure with varied size openings between strands. The meshcan be coated with an elastic polymer film in whole or in part, or withanother material, so as to reduce in size or eliminate the openingsbetween strands. The coated mesh may be partially or totally occlusiveto flow of fluid or particles therethrough. In some embodiments themetal strands may be superelastic alloys comprised of radiopaque alloyconstituents. In some preferred embodiments a metal strand is comprisedof nickel-titanium-platinum or nickel-titanium-tantalum alloy. Inaddition, some or all of the strands may be comprised of materials otherthan metal including but not limited to engineering polymers such asPEEK (polyetheretherketone), liquid crystal, polyamide, or polyester;ceramics; glass-ceramics; metallic glasses; or other materials known inthe art. In some embodiments the aforementioned materials can becomprised of radiopaque filler materials. In some embodiments thestrands are homogeneous in the sense that they are not comprised ofseparate layers. It is further understood that the cross section of someor all of the strands can be round, ovoid, square, rectangular,triangular, irregular, symmetrical, non-symmetrical, or other shapes.

FIGS. 1A to 1C illustrate conceptually partial plan views of braidedmeshes having radiopaque and non-radiopaque wires in accordance with thepresent invention. For clarity only the braided wires along half of thebraided perimeter of the tube are shown. Braided wires arranged belowthe illustrated wires are not shown. Also for clarity the radiopaquewires in FIGS. 1A to 1C are shown as having slightly increased diameteras compared to non-radiopaque wires, although it is understood that therelative sizes of the radiopaque and non-radiopaque filaments may not beas illustrated and generally will be determined according to theteachings below. Further, strands are generally illustrated asintersecting at angles of approximately 900, although it is understoodthat within the scope of the invention strands can intersect or overlapat any angle.

In FIG. 1A braided tubular mesh 10 is comprised of interwoven wires 12and 14. Non-radiopaque wires 12 comprise the majority of the wires andtwo sets of adjacent pairs of radiopaque wires 14 are interwoven withthe non-radiopaque wires 12. Braided tubular mesh 10 has a number ofpores 16 defined by the wires, and each pore has a size, the pore sizedefined as the area bounded by the wires forming the perimeter of thepore. Braided tubular mesh 10 can be formed of a variety of materials.Metal wires are preferred, and superelastic nitinol is particularlypreferred for the non-radiopaque wires 12. Braided tubular mesh 10 has adiameter D, which is the diameter of the braided tubular mesh at rest infree space. Diameter D is determined by braiding processing parametersand wire diameters used. Heat treatments may be used to help stabilizediameter D, especially when wire materials such as nitinol are used. Abraid comprised of nitinol wire is typically heat set at 400 to 600° C.for 1 to 60 minutes to stabilize the braid diameter. In a preferredembodiment nitinol wire is heat set at 425° C. for 20 minutes tostabilize the braid diameter. Non-nitinol wires may be annealed attemperatures that will stress relieve or even recrystallize thematerials in order to stabilize the tubular braid diameter. It isunderstood that self-expanding or self-contracting devices can becomprised of braided tubular mesh 10. Self-expanding devices are devicesin which, during use, braided tubular mesh 10 is compressed andsubsequently allowed to expand without application of forces external tothe mesh for causing expansion. Self-contracting devices are devices inwhich, during use, braided tubular mesh 10 is expanded and subsequentlyallowed to contract without application of forces external to the meshfor causing contraction. It is advantageous to construct self-expandingor self-contracting devices at least in part from wires that haveelastic strain limits higher than the elastic strains generated in thewires during use of these devices, and to process the wires so as toretain or enhance the elastic strain limits of the wires chosen. Deviceswhich are neither self-expanding nor self-contracting may also becomprised of braided tubular mesh 10. Devices of the invention may alsobe comprised of braided tubular mesh or strands which deform uponexpansion or contraction. The strands of such devices may be processedor chosen such that the elastic strain limit of the strands are lessthan the elastic strains generated in the strand during use of thedevice.

FIG. 1B illustrates braided tubular mesh 10 comprised of a singleradiopaque wire 14 interwoven with non-radiopaque wires 12 and FIG. 1Cillustrates braided tubular mesh 10 comprised primarily of radiopaquewires 14 interwoven with a minority of non-radiopaque wires 12. It isunderstood that multiple combinations of interwoven radiopaque andnon-radiopaque wires 14 and 12 are possible within the scope of theinvention, and that the number, proportion, and positioning ofradiopaque and non-radiopaque wires within the mesh will be chosen basedon the desired device functional and other requirements.

FIG. 2 illustrates conceptually a side view of filter 20 formed from abraided tubular mesh 10 comprised of interwoven radiopaque andnon-radiopaque wires 12 and 14 in accordance with the present invention.For clarity the wires on the back side of the filter are not shown.Filters similar to that shown in FIG. 2 can be made by enlarging a porein the side wall of the braid using a tapered mandrel and stabilized inthe desired shape by heat treating on a mandrel. Processing details formaking a filter using these methods are disclosed in U.S. Pat. No.6,325,815 B1 to Kusleika et al., entitled “Temporary Vascular Filter”,the contents of which are incorporated herein by reference. In filter20, radiopaque wires 14 are bunched at the opening of the filter,providing improved visibility under fluoroscopy of the perimeter 26 ofmouth 24 of the filter. In an alternate embodiment radiopaque wires 14are bunched distal to mouth 24 of the filter, providing improvedvisibility under fluoroscopy of the portion of the filter apposing avessel wall during use. Radiopaque wires 14 also extend throughout thebody 22 of the filter mesh, providing visibility under fluoroscopy tothe body of the filter.

FIG. 3 illustrates conceptually a method for forming filter 20 frombraided tubular mesh 10 comprised of interwoven radiopaque andnon-radiopaque wires 12 and 14 in accordance with the present invention.Pore 35 is chosen as the pore to enlarge into mouth 24 of filter 20.Pore 35 is chosen specifically such that radiopaque wires 14 a will bebunched along the perimeter 26 of filter mouth 24 during the filterforming process. In FIG. 3, pore 35 is located 3 pores from theintersecting pore 38 of radiopaque filaments 14 a. In one example,braided tubular mesh 10 is comprised of 36 wires and has a diameter D of3 mm before forming into filter 20. Two pairs of radiopaque wires 14 aare interwoven into tubular mesh 10 as illustrated in FIG. 3, and theremaining 32 wires are non-radiopaque nitinol. Pore 35 is located 8pores from intersecting pore 38 of radiopaque filaments 14 a. In anotherexample, braided tubular mesh IO is comprised of 72 wires and has adiameter D of 7 mm before forming into filter 20. Two pairs ofradiopaque wires 14 a are interwoven into tubular mesh IO as illustratedin FIG. 3, and the remaining 68 wires are non-radiopaque. Pore 35 islocated 15 pores from intersecting pore 38 of radiopaque filaments 14 a.It is understood that the location chosen for piercing braided tubularmesh 10 comprised of interwoven radiopaque and non-radiopaque wires 12and 14 will vary within the scope of the invention and will depend onthe application contemplated and results desired.

When adding radiopaque wires to a mesh comprised primarily ofnon-radiopaque wires it is often desired to increase the diameter of theradiopaque wire relative to the diameter of the non-radiopaque wire soas to increase the visibility of the radiopaque wire under fluoroscopy.FIG. 4A illustrates the effect of adding a larger wire 42 to a mesh 40,wherein the pore sizes 45 adjacent to the larger wires are increased inarea as compared to pore sizes 47 in the portion of the mesh comprisedof smaller wires 44 due to the presence of the larger wire 42 relativeto the adjacent smaller wires 44 in the mesh. For certain applications,including some filter devices, large pores in the braid can beunacceptable because the large pores will allow large emboli to passthrough the filter.

FIG. 4B illustrates braided tubular mesh 40 comprised of a large wire 42and multiple smaller wires 44 having uniformly sized pores 48, aconfiguration preferred for filtering applications such as for distalembolic protection devices. The uniformly sized pores illustrated inFIG. 4B are achieved by using similar stiffness wires in the mesh. Auseful index of wire stiffness is EI, where E is the Young's modulus ofthe wire material, I is the second moment of area of the wire, and EI isthe mathematical product of the two. In a preferred embodiment of thedevice, the largest EI of wires used in the device is no more than 5times the smallest EI of wires used in the device. In a more preferredembodiment of the device, the largest EI of wires used in the device isno more than 4 times the smallest EI of wires used in the device. In afurther preferred embodiment of the device, the largest EI of wires usedin the device is no more than 2 times the smallest EI of wires used inthe device. In a further preferred embodiment of the device, the largestEI of wires used in the device is no more than 1.5 times the smallest EIof wires used in the device. In a further preferred embodiment of thedevice, the largest EI of wires used in the device is no more than 1.3times the smallest EI of wires used in the device.

Referring again to FIG. 4A, the area of pore 45 a adjacent to large wire42 is much greater than the average area of the five pores 47 a, 47 b,47 c, 47 d, and 47 e serially adjacent to pore 45 a. For convenience wehereby define the average area of the five pores 47 a, 47 b, 47 c, 47 d,and 47 e serially adjacent to pore 45 a as the mesh pore size. Thisdefinition allows us to apply the inventive teachings herein to variousfilter shapes with varying pore sizes, including tapered filters wherethe pore size varies along the length of the filter, such as the filterillustrated in FIG. 2. In a preferred embodiment of the mesh at rest infree space, the size of pore 45 a adjacent to large wire 42 is no morethan 5 times larger than the mesh pore size. In a more preferredembodiment of the mesh, the size of pore 45 a adjacent to large wire 42in the mesh at rest in free space is no more than 4 times larger thanthe mesh pore size. In a further preferred embodiment of the mesh, thesize of pore 45 a adjacent to large wire 42 in the mesh at rest in freespace is no more than 3 times larger than the mesh pore size. In afurther preferred embodiment of the mesh, the size of pore 45 a adjacentto large wire 42 in the mesh at rest in free space is no more than 2times larger than the mesh pore size. In a further preferred embodimentof the mesh, the size of pore 45 a adjacent to large wire 42 in the meshat rest in free space is no more than 1.5 times larger than the meshpore size. In a further preferred embodiment of the mesh, the size ofpore 45 a adjacent to large wire 42 in the mesh at rest in free space isno more than 1.2 times larger than the mesh pore size.

To achieve the uniform pore size illustrated in FIG. 4B variousapproaches can be used to match wire stiffnesses. In one embodiment atubular braided mesh of monofilament 52 (see FIG. 5A) stainless steelwires incorporates an interwoven monofilament wire having a largerdiameter than the stainless steel wires with the Young's modulus of theinterwoven larger wire less than that of stainless steel. Suitablechoices of material for the larger wire include gold and platinum (seeTable 1 below). The lower modulus of gold and platinum relative tostainless steel will offset the larger diameter of the radiopaque wiresuch that the calculated EI's of the radiopaque and non-radiopaque wireswill be equal or similar.

TABLE 1 Material Young's Modulus, E (GPa) Gold  78 Nitinol (Austenitic)75-83 Platinum 168 Tungsten 411 Tantalum 186 Stainless Steel 199

In an alternate embodiment, multifilament wires 53 can be used (see FIG.5B). The diameter of each individual filament 54 of a multifilament wireis smaller than the overall diameter of the wire 53 and this allowshigher modulus materials to be incorporated into some or all of thefilaments 54 of a larger multifilament wire 53. For example, braidedtubular mesh comprised of nitinol monofilament wires could incorporateone or more interwoven multifilament wires comprised of gold, platinum,tungsten, tantalum, or other radiopaque materials. In one embodiment ofa multifilament wire more than one filament is twisted into a helicalshape around a central filament. In another embodiment of multifilamentwire 53 individual monofilaments are interwoven into the braid adjacentto each other as shown in FIG. 5E. It is understood that many othercombinations of filaments can be devised by one skilled in the artwithin the scope of the invention.

In a further embodiment, FIGS. 5C and 5D illustrate slotted wire 56 inwhich monofilament wire 57 has had material removed in the form of slots58, for example by grinding. Slots 58 have opposing faces 59 and due tomaterial having been removed from the perimeter of the wire to formslots 58 the overall modulus of wire 56 is reduced.

One example of deriving uniform pore size by matching wire stiffnessesis as follows. Tubular braided mesh is comprised of 36 Nitinolmonofilament wires of 0.003″ (0.0076 cm) diameter. It is desired toimprove the visibility of the mesh by substituting a monofilamentcircular cross section tungsten wire for one of the nitinol wires, andto do so without significantly changing the pore size of the mesh. Theappropriate diameter of the tungsten wire is calculated as shown below.I/ρ=M/(E×I)

-   -   Where ρ=the density of the material in bending, M=the bending        moment, and E & I are as defined above. Equating the bending        moments of nitinol and tungsten wires yields:        (E _(w) ×I _(w))/ρ_(w) =M=(E _(NiTi) ×I _(NiTi))/ρ_(NiTi) and        I=(πd ² L ³ρ)/(48g)    -   Where π=3.14159, d=monofilament diameter, L=the unsupported        transverse length of the filament, and g=the gravitational        constant        By combining terms:        E _(w)×(πd _(w) ² L _(w) ³ρ_(w))/(48g ρ _(w))=E _(NiTi)×(1td        _(NiTi) ² L _(NiTi) ³ p _(NiTi))/(48g p _(NiTi))        and by eliminating like terms:        E _(w) ×d _(w) =E _(NiTi)×^(d) _(NiTi) ²        Substituting known values and solving for d_(w) yields        d _(w)=0.0013″(0.0033 cm)

In another example, the appropriate diameter of gold wire to besubstituted into the mesh, using the same calculation as above exceptsubstituting into the equations the material parameters of gold in placeof the parameters of tungsten, would be d_(Au)=0.0031″ (0.0079 cm).

In yet another example, the appropriate diameter of nitinol monofilamentwires to be braided with 0.0024″ (0.0061 cm) outer diameter 1×7 strandedtungsten wire (constructed from a central monofilament of tungstensurrounded by a ring of 6 tungsten monofilaments of the same diameter asthe central filament) into tubular braided mesh having uniform pore sizeis calculated as follows. The equations above are used to calculate EIfor each individual tungsten filament (having a filament diameter of0.0008″ (0.002 cm) in this example). The EI of the stranded wire isapproximated as seven times that of one tungsten monofilament (assumingthe friction between filaments is small compared to the bendingstiffness of the filaments, therefore no adjustment is made forfriction). The equations above are solved for d_(NiTi) by equating EIfor the nitinol wire with the calculated EI for the tungsten strandedwire. In this example d_(NiTi) is approximately equal to 0.0047″ (0.012cm). It is understood that improved calculations for the stiffness ofmultifilament wire can be employed as part of these calculations.Improved calculations may account for frictional forces between strands,non-linear configuration of some or all of the strands, or otherfactors.

Another means for achieving uniform pore size braided mesh comprised ofsome radiopaque wires is by matching radiopaque and non-radiopaque wirediameters. The smaller the distance between interwoven radiopaque andnon-radiopaque wires the greater the variation in pore size caused bydiffering wire diameters. In a preferred embodiment of the device, thelargest diameter of wires used in the device is no more than 5 times thesmallest diameter of wires used in the device. In a more preferredembodiment of the device, the largest diameter of wires used in thedevice is no more than 4 times the smallest diameter of wires used inthe device. In a further preferred embodiment of the device, the largestdiameter of wires used in the device is no more than 2 times thesmallest diameter of wires used in the device. In a further preferredembodiment of the device, the largest diameter of wires used in thedevice is no more than 1.5 times the smallest diameter of wires used inthe device. In a most preferred embodiment both the wire diameter andthe wire stiffness of both the radiopaque and non-radiopaque wires aresimilar.

A method of using a device made from the inventive mesh is as follows.An embolic protection device, made using methods similar to thosediscussed in connection with FIG. 2, is delivered percutaneously to aregion of interest in the body of a patient using methods known in theart. Optionally a catheter is used to deliver the filter to the regionof interest. Fluoroscopy is used by the operator to visualize the mouthand the body of the filter to ascertain that the filter is positionedappropriately in relation to a treatment or diagnostic site, forexample, positioned such that the mouth of the filter is distal to astenosis in an artery, and also by example, positioned such that thebody of the filter is in a healthy region of vessel suitable for use asa landing zone for the filter. The filter is then deployed and thecatheter (if used) is removed from the vicinity of the filter. Theoperator uses fluoroscopy to ascertain that the mouth of the filter isadequately deployed against the vessel wall with no gaps, distal to thelesion, and proximal to any important side branch vessels. Radiopaquecontrast media may be injected at this time or at any time to assistwith visualization of the patient's anatomy. The treatment site istreated, for example by dilating a lesion with a balloon dilatationcatheter and by deploying a stent or drug eluting stent at the treatmentsite, although other methods known in the art can be used.

After or during treatment or both, the operator may visualize the mouthand body of the device and may adjust the position of the device toassure, for example, that the device is properly located along thelength of the vessel and properly apposed to the vessel wall. Aftertreatment the device is recovered. Optionally a catheter is used duringthe recovery process. At least a portion of the filter is drawn into therecovery catheter (if used) and the mouth and body of the filter areobserved under fluoroscopy to ascertain when the device is sufficientlydrawn into the catheter. If difficulty is encountered while drawing thefilter into the catheter the devices are again imaged under fluoroscopyand the cause of the difficulty is diagnosed in part by observing theradiopaque portions of the device. The filter (and recovery catheter ifused) are then withdrawn from the vessel. If resistance to withdrawal isencountered then the devices are imaged under fluoroscopy and the causeof resistance is determined and eliminated.

While this document has described an invention mainly in relation tobraided tubular mesh used for embolic protection filtering devices usedin arteries, it is envisioned that the invention can be applied to otherconduits in the body as well including veins, bronchi, ducts, ureters,urethra, and other lumens intended for the passage of air, fluids, orsolids. The invention can be applied to other devices such as vena cavafilters, stents, septal defect closure devices, and other devicescomprised of mesh having the benefits described above.

While the various embodiments of the present invention have related toembolic protection filtering devices, the scope of the present inventionis not so limited. Further, while choices for materials andconfigurations have been described above with respect to certainembodiments, one of ordinary skill in the art will understand that thematerials described and configurations are applicable across theembodiments.

The above description and the drawings are provided for the purpose ofdescribing embodiments of the invention and are not intended to limitthe scope of the invention m any way. It will be apparent to thoseskilled in the art that various modifications and variations can be madewithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A device for filtering emboli from blood flowingthrough a lumen defined by the walls of a vessel in a patient's body,comprising: a filter element being expandable from a collapsedconfiguration when the filter element is restrained to an expandedconfiguration when the filter element is unrestrained, wherein thefilter element comprises a mesh comprising strands, each strand having across-sectional dimension, the mesh comprising at least one radiopaquestrand and at least one non-radiopaque strand, the at least oneradiopaque strand and the at least one non-radiopaque strand each havingdifferent cross-sectional dimensions, and wherein a Young's modulus ofthe at least one radiopaque strand is different than a Young's modulusof the at least one non-radiopaque strand.
 2. The device of claim 1,further comprising an elongate support member and wherein the filterelement is carried on a portion of the elongate support member.
 3. Thedevice of claim 1, wherein the filter element has proximal and distalportions and a central portion, the filter element having a shape in theexpanded configuration which defines a cavity having a proximal facingopening.
 4. The device of claim 3, wherein the filter element has aproximal facing opening portion and this portion is radiopaque.
 5. Thedevice of claim 1, wherein the filter element is self-expanding.
 6. Thedevice of claim 1, wherein the mesh is tubular.
 7. The device of claim6, wherein the mesh is braided.
 8. The device of claim 1, wherein theYoung's modulus of the at least one radiopaque strand is less than theYoung's modulus of the at least one non-radiopaque strand.
 9. The deviceof claim 1, wherein the Young's modulus of the at least one radiopaquestrand is greater than the Young's modulus of the at least onenon-radiopaque strand.
 10. The device of claim 1, wherein the at leastone radiopaque strand has a larger cross-sectional dimension than the atleast one non-radiopaque strand.
 11. The device of claim 1, wherein thelargest cross-sectional dimension of a strand is no more than two timesthe smallest cross-sectional dimension of any other strand.
 12. Thedevice of claim 1, wherein each strand has an index of wire stiffnessEI, where EI is the mathematical product of the Young's modulus (E) andthe second moment of area (I), and wherein the EI of all strands in themesh is no more than 5 times the EI of the strand having the smallest EIof any of the strands.
 13. The device of claim 1, wherein each strandhas an index of wire stiffness EI, where EI is the mathematical productof the Young's modulus (E) and the second moment of area (I), andwherein the EI of all strands in the mesh is no more than 4 times the EIof the strand having the smallest EI of any of the strands.
 14. A meshcomprising strands, each strand having a diameter, the mesh comprisingat least one radiopaque strand and at least one non-radiopaque strand,the at least one radiopaque strand and the at least one non-radiopaquestrand each having different cross-sectional dimensions, and wherein aYoung's modulus of the non-radiopaque strand is different than a Young'smodulus of the radiopaque strand.
 15. The mesh of claim 14, wherein themesh is tubular.
 16. The mesh of claim 15, wherein the mesh is braided.17. The mesh of claim 14, wherein the Young's modulus of the at leastone radiopaque strand and the Young's modulus of the at least onenon-radiopaque strand differ by 10 percent or more.
 18. The mesh ofclaim 14, wherein the Young's modulus of the radiopaque strand and theYoung's modulus of the non-radiopaque strand differ by 20 percent ormore.
 19. The mesh of claim 14, wherein the at least one radiopaquestrand is made of homogeneous metal or metal alloy.
 20. The mesh ofclaim 14, wherein the Young's modulus of the at least one radiopaquestrand is less than the Young's modulus of the at least onenon-radiopaque strand.
 21. The mesh of claim 14, wherein the Young'smodulus of the at least one radiopaque strand is greater than theYoung's modulus of the at least one non-radiopaque strand.
 22. The meshof claim 14, wherein the at least one radiopaque strand has a largerdiameter than the at least one non-radiopaque strand.